Basking shark

The basking shark is the world's second largest species of shark (currently extant), dwarfed only by the whale shark (Rhincodon typus), and is the largest fish to be found in the Mediterranean Sea. Like the whale shark and the megamouth shark (Megachasma pelagios), the basking shark is a filter feeder, allowing massive amounts of water to enter its mouth, then using gill rakers to filter out small organisms, such as plankton, small crustaceans, and fish eggs. The shark will occasionally close its mouth to swallow the food collected in its gill rakers. The basking shark is thought to be able to process about 6000 litres of water per hour in this method. The whale, basking, and megamouth sharks are the only sharks which filter feed. Unlike the whale and megamouth sharks however, the basking shark relies only on the flow of water through its mouth generated by its swimming to catch food. The other two species assist this flow through pumping or suction.

The basking shark takes its name (and another, sunfish) from its habit of cruising along just below the surface of the water, while feeding, usually with its triangular dorsal fin exposed to the air (thus basking in the sun). The basking shark has also been referred to as the big mouth shark (due to its enormous mouth), bone shark, elephant shark (due to its size), liver shark, and sailfish. Basking sharks have massive livers, which can account for up to 25% of their body weight, and are used to give the creatures a near-neutral buoyancy. The shark can weigh up to around 3600 kilograms. The longest recorded basking shark is 15.2 metres, though the average length of the species is believed to be about 9 metres. The shark's five pairs of gill slits are massive, almost completely encircling its head. The gills are covered with between 1000 and 1300 gill rakers of about 10cm in length each. The massive mouths of the basking shark contain hundreds of seemingly useless teeth, likely a leftover from before the fish evolved to eat the way it does now (similar to the human appendix).

In the past, sightings of multiple basking sharks travelling single file near the surface have caused sailors to claim the creatures were sea serpents. The basking shark's head is noteably smaller than one might expect compared to the rest of its body. Carcasses washed up on shores or pulled in by fishing equipment have been cause for many to think the sharks were an unknown species. The basking shark has small eyes and a very short, conical snout. The shark's dorsal region can be coloured a dark greyish-brown or near-black, with the ventral region having an off-white colour with blotches of darker colour here and there. The species was first described in 1765 based on a specimen found off the coast of Norway. The basking shark was originally classified as Squalus maximus.

The basking shark is a sluggish swimmer, moving its entire body from side to side in order to propel itself (rather than just its tail, as some sharks do) at a mere 5 kilometres per hour. The basking shark can, however, move very quickly in short bursts and, according to some, is able to leap out of the water (though it's possible those observing the sharks leaping out of the water had misidentified them). Basking sharks have been observed travelling alone, in pairs, and in schools of up to one hundred members. Basking sharks apparently move in pursuit of large deposits of plankton to feed on. Basking sharks can be found off the coasts of North America (from Baja California to southern Alaska in the west and Florida to southern coastal regions of Canada in the east), South America (specifically the southern coasts), Europe, Australia (once again the southern coasts), South Africa, New Zealand, Japan, and China. In addition to this, basking sharks can be found along the Gulf Stream in the Atlantic Ocean and inside the Red Sea. Basking sharks prefer temperate waters and spend most of their time not far from the shore but are willing to enter into deeper, farther offshore waters as well.

Basking sharks apparently migrate (in groups segregated by sex) throughout the year, disappearing from the regions they're usually sighted in during the winter. At the time of this writing, it's unknown where exactly the sharks go during the winter months. Two theories seem to be popular amongst the scientific community: One is that the sharks shed their gill rakers during the winter and go into a state of hibernation in deepr waters until spring, when new rakers have grown. The other theory is that, again, their gill rakers are shed and the sharks venture into deeper waters to become benthic (near bottom) feeders (which might also explain why basking sharks still have teeth) until their gill rakers grow back.

Little is known about the breeding habits of the basking shark. Only one female carrying an embryo has ever been recorded at the time of this writing. The female reportedly gave birth to five living and one stillborn shark pups, all of which ranged between 1.5 and 2 metres in length. It's unknown at what age the basking shark reaches sexual maturity, though the species is known to grow slowly. The gestation period of the shark is believed to be around 3.5 years and the species is thought to go through aplacental viviparity (this is the process of the young hatching from their eggs while still inside the womb and feed on unfertilized eggs and/or each other, depending on the species, until they're born as no placenta is present) during this time. The pups swim away from their mother immediately after birth: There's no postpartum care for them from the mother. Juvenile basking sharks have a longer, hook-like snout, which is thought to assist the young sharks in feeding while in the womb and after being born by increasing the flow of water into the mouth. The junveniles' snouts will shorten themselves as the sharks grow.

The basking shark is a very unaggressive species, tolerant of both boats and divers around it, though they have been known to attack boats after being harpooned. Humans should avoid contact with the skin of the basking shark, as dermal denticles have been known to cause some harm. The exact population of the species is currently unknown, though believed to be decreased or at least vunerable due to hunting. Currently, only fishers from Japan and China hunt the basking shark. An average size basking shark can yield about a ton of meat and 380 litres of oil. The fins are used for shark fin soup. Fresh fins can fetch up to $1,000 in Asian markets, while dried and processed fins generally sell for around $350 per pound. The livers of the basking shark are sold in Japan as a health food and an aphrodisiac.

Aside from humans, the only other species the basking shark seems to have to worry about are the cookiecutter shark (Isistius brasiliensis) and the sea lamprey (Petramyzon marinus). Cookiecutter sharks have been known to attack basking sharks by biting off pieces of their target's flesh with their suction cup-like mouths. Sea lampreys are unable to penetrate the thick, denticle-sporting skin of the basking shark, but can pose enough of a nuisance to encourage the shark to rub against something in order to detach the lamprey. Removing sea lampreys might also be cause for basking sharks to leap out of the water, assuming they really can do that.

One of the largest species of sharks (Cetorhinus maximus), so called from its habit of basking in the sun; the liver shark, or bone shark. It inhabits the northern seas of Europe and America, and grows to a length of more than forty feet. It is a harmless species.